The Effect of Time of Top-Dressing on Uptake of Phosphorus and Potassium by an Established Stand of Alfalfa1

William A. Seay and

M. E. Weeks2

Abstract

Abstract

Plots of established alfalfa were top-dressed with radioactive superphosphate and half the plots received potash. Top-dressing dates varied from September to the following June. Entire plants were sampled at various periods after top-dressing and divided into tops, crowns, and roots for analyses.

Conclusions were (1) P and K are translocated to crowns from roots and tops during autumn, (2) top-dressed P is taken up by alfalfa even in the winter or dormant season, (3) in spring a rapid translocation of P and K from roots and crowns to tops occurs, (4) K fertilization does not affect P uptake from soil by alfalfa, (5) P fertilization does not significantly affect K uptake from soil by alfalfa although trends are more suggestive than the effect of K fertilization on P uptake, and (6) top-dressed P was taken up to a greater extent from Hagerstown silt loam than from Nicholson silt loam which was expected in that chemical soil tests showed more available P in the Nicholson.

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